Register Now

In order to be able to post messages on the The Planted Tank Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:

Password

Please enter a password for your user account. Note that passwords are case-sensitive.

Password:

Confirm Password:

Email Address

Please enter a valid email address for yourself.

Email Address:

OR

Log-in

User Name

Password

Remember Me?

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Additional Options

Miscellaneous Options

Automatically parse links in text

Automatically retrieve titles from external links

Topic Review (Newest First)

08-03-2016 03:05 AM

mistergreen

It should work. You would need a different library for your display.

Sent from my iPad using Tapatalk HD

08-01-2016 05:49 PM

Killavolt

This has been a long thread, hopefully it can still garner some activity.

What would need to be done to make this code work with an Arduino Mega 2560 and a ITDB02 or Nextion TFT screen?

I'm wanting to building my own LED lighting controller and I think having a PAR meter built in would be a great feature. This way it could display the PAR value during the different light cycles like sunrise/sunset etc.

Dear Mr. Green,
I see you've been through a long journey of building a PAR sensor. May I ask if you have complete instructions on hand? If yes I'd really appreciate if you could share them.

If not, could you give me few pointers. I have few questions here. What is the purpose of Cosine diffuser and how do you use it? Is the Photodiode VTB8441BH submersible? I was thinking to put the sensor into the aquarium for constant monitoring. Will this work with Miniature Solar Cell - BPW34? I'd prefer to use the latter one since it is much smaller.

Also, what is the algorithm to calculate the PAR value from the sensor reading?

Thanks a lot,
Ruben

Hi, It's best to build a water proof housing of the vtb8441bh.
I've also added spectral light filters to the diode to further help with PAR calculations. You can find it here

Dear Mr. Green,
I see you've been through a long journey of building a PAR sensor. May I ask if you have complete instructions on hand? If yes I'd really appreciate if you could share them.

If not, could you give me few pointers. I have few questions here. What is the purpose of Cosine diffuser and how do you use it? Is the Photodiode VTB8441BH submersible? I was thinking to put the sensor into the aquarium for constant monitoring. Will this work with Miniature Solar Cell - BPW34? I'd prefer to use the latter one since it is much smaller.

Also, what is the algorithm to calculate the PAR value from the sensor reading?

Thanks a lot,
Ruben

07-02-2015 03:13 AM

rottison

mistergreen now that I have my par meter built I need to calibrate it my local club has a apogee meter I can use. Do you do any thing special to calibrate? And how do you calibrate the par meter normaly?

06-11-2015 03:54 AM

rottison

that is how I thought it went also just wanted to make sure before it was glued down

06-11-2015 02:39 AM

Quizcat

I believe that the diffuser goes into the bottom of the jar first, then you put the filters between the acrylic diffuser and the photo diode, so that light passes first through the diffuser, then through the filters, where it hits the screen of the photo diode. Correct me if I'm wrong Mistergreen.

so in the morning I will make it more permanent but I have 3 colored ronco disk cut to fit the jar and just dropped in then I will glue the photo optic to the diffuser and drop that in and dab a bit of silicon on the edges to hold it in place few hours drying time I should be almost done.

06-11-2015 01:16 AM

rottison

so in the morning I will make it more permanent but I have 3 colored ronco disk cut to fit the jar and just dropped in then I will glue the photo optic to the diffuser and drop that in and dab a bit of silicon on the edges to hold it in place few hours drying time I should be almost done.

06-10-2015 11:42 PM

mistergreen

The order of the light filters doesn't matter but I would put the diffuser on top.

06-10-2015 08:48 PM

rottison

mistergreen does it matter what filter or disk goes to the bottom of the jar fist or in what order

06-07-2015 03:35 PM

mistergreen

hmm, interesting. The only thing I can think of is the variance on the voltage regulator and resistors in that chain to the atmega that would give us different results. So it would vary from batch to batch.

The regulator is outputting to 4.99V (middle & right pin)and the resistor by the atmega is 10.05K.

Yeah, there might be too many variance to get an exact number. I guess the only way to calibrate is to use another calibrated CEP with light sensor or a PAR sensor.

06-07-2015 01:40 PM

Quizcat

I think that O2Surplus envisioned that any calibrated CEP, once calibrated to a PAR meter, and the values known, will calibrate exactly the same way each time via the 10K resistor method, the 10K resistor eliminating the variability of the sensor itself. Then, because of the standardization of the sensor input to 10K, only one calibrated CEP would be necessary for anyone to calibrate their individual CEP using the 10K resistor method.

But, having taken some readings from my own CEP, the theory does not seem to correlate to readings Mistergreen obtained from his calibrated CEP.

I confirmed the value of my 10K ohm resistor that was put across the sensor terminals, and it is 9.97K ohms. Close enough, tolerance of about 3%, but it occurs to me that there may be variabilites in all the components within the circuits of individual CEPs to make universal calibration through a mathematical formula almost impossible as these variabilities add up...unless there is some kind of conversion factor that can be used to acount for the actual values of components used in individual CEPs. Take my 15K ohm resistor for example. Mine reads 11.94K, and not 15K.

06-07-2015 01:10 PM

Quizcat

Here are the results...

I was very fortunate, in that I had an Electronics Rainbow kit for my grandson that I was able to find a 10K ohm resistor.

So, I wrapped black electrical tape around the leads of the resistor so that my holding it did not change the resistance.

First, I tested the CEP that had been calibrated to Mistergreen's commercially produced PAR meter, we will call it CEP #1, and got the following result on the LDC screen of the CEP:

I tested several ways, from the soldered pins of the jack, and also from the two terminals of the green block where the Sensor wires connect, holding the resistor with my fingers, making sure to only hold the resistor through the black electrical tape I applied to the resistor. I also took readings holding the resistor with a set of tweezers grasping the black tape area. But, I don't have a set of plastic tweezers, which would have been preferable to perform this test. So, I hope that the black electrical tape did the job to isolate the resistor from any effects from my touching it. The readings were taken multiple times, and the results were always consistent.

I also tested the two CEPs that have only been calibrated by me using the resistance method, and not through a light emitter via a commercially produced PAR meter. These CEPs were calibrated by putting a probe on the top pad of the 15K ohm resistor, and touching the other probe to pin #1 and #2 on the 10K POT. You may recal that CEP #2 calibrated
to 27.46 ohms, and CEP #3 calibrated to 27.5K ohms using this method, and were calibrated to closely match the results using this method from CEP #1, which had been calibrated using a PAR meter by Mistergreen.

When using the 10K ohm resistor touched to the input of the sensor terminals, the CEPs returned the following values on the LCD screen:

CEP #2 previously calibrated to 27.46K using the resistance method between the 15K resistor and terminals 1 & 2 at the POT:
LCD Reading =
Indoor = 3813 using 10K resistor at the input terminals of the sensor
Outdoor = 3458 using 10K resistor at the input terminals of the sensor

CEP #3 calibrated to 27.5K using the resistance method between the 15K resistor and terminals 1 & 2 at the POT:
LCD Reading =
Indoor = 3819 using 10K resistor at the input terminals of the sensor
Outdoor = 3463 using 10K resistor at the input terminals of the sensor

CEO #2 and CEP #3 are consistent with the results returned from CEP #1, the one calibrated to Mistergreen's PAR meter, but slightly off from one another because the POT is pretty touchy, and it's hard to get that fine of an exact adjustment using a screw driver.

I did not change the POT adjustments of CEP 2 & 3 because they appeared to mimmick the adjustment I made via the top resistor pad and the POT terminals previously made, versus the 10K resistor method, so I left them alone, right where they were.

I don't know why the values I obtained versus the values obtained by Mistergreen on his CEP using the 10K resistor at the sensor terminals are so far off from one another.

Could it have anything to do with my 15K resistor value being measured at 11.94K versus 15K? If so, then perhaps a reading of the 15K resistor would be in order before calibrating using the 10K resistor method, and some kind of conversion factor could be applied to acheive actual calibration based on the actual 15K resistor value of any random CEP.

06-07-2015 03:49 AM

Quizcat

I'll try this as soon as I can. Because I live in a rural area, it may take a few days to come up with a 10K resistor. They just closed our Radio Shack for good. I'll check my stash to see if I have one, but if not, then I'll have to order one from Mouser. So, it may be a few days before I can get back to you guys. But, if it works, it's a wonderful stroke of genious!

Now, one question, regarding my calibrated CEP, the PCB is permanently stuck to the back wall of a plastic cabinet via double stick tape, and can not be removed, it's like concrete. The photo diode is connected to the PCB via a power jack/plug via wire extensions between the jack and the input for the sensor at the PCB. See the white wire on the left? The sensor connects to the PCB through the jack. Power, is the Red/Black wire on the right, connected to power on the PCB through a power plug/jack.

Can I just unplug the sensor, unplug power, and put the 10K resistor across the center pin and ground at the sensor's jack terminals, and be good to go, or will having the jack in the mix throw things off with respect to the jack and wire extenstions to the PCB adding resistance? And, if accessing the sensor terminals through the jack is a problem, technically speaking, then it just makes it a little more difficult to access the sensor terminals inside the cabinet to make the connections, due to the confined space inside the cabinet, and because the CEP can't be removed. It can be done, no problem, but it would make it easier and quicker to connect at the jack if it won't throw everything off.

I've got an idea that should make calibrating the new meters against the known calibrated unit really easy. You can use the voltage signal on A0 and the PAR number output to the Lcd to calibrate the units. It's a simple matter of turning the sensor circuit into a voltage divider by using a resistor instead of the photo diode.

1.) Start by disconnecting the photo diode from the known good calibrated unit.

2.) Install a 10K resistor across the photo diode connection points at the CEP PcB.

3.) Power up the CEP and take note of the PAR number displayed on the Lcd. This PAR number will be your reference.
4.) Reinstall the photo diode and set this CEP meter aside.

5.) Grab one of the new units and install the same resistor across the photo diode connections.

6.) Power up the unit and adjust the pot until the Par reading is the same as the original calibrated unit.

7.) Perform the same steps above on any remaining uncalibrated units.

Following these steps should set up all your CEP's to be identically calibrated. The only variable left will be slight electrical variations between the photo diodes.